(1) Field of the Invention
The present invention relates generally to an apparatus for mixing and dispersing materials, and more particularly to an apparatus for dispersing and grinding materials by means of a particulate grinding medium.
(2) Background Information
Generally, a conventional dispersing and grinding apparatus employs a rotary agitator, such as discs, flights, stirring rods or the like, disposed within a vessel. In use, a material which is to be dispersed and ground is charged into the vessel through an inlet. A particulate grinding medium is added to the vessel and assists in grinding the material in conjunction with the rotating action of the agitator. As the agitator rotates, the mixture of material and grinding medium is agitated and advanced lengthwise through the vessel while mixing and dispersing the material. The dispersed and ground material is discharged through an outlet at the other end of the vessel, and the grinding medium is separated from the material and retained within the vessel for re-use.
In this type of apparatus, the mixture consisting of the grinding medium and the material flows lengthwise through the vessel at a relatively high velocity gradient, and the flow velocity of the mixture at the downstream end near the outlet is higher than at the upstream end near the inlet. As a consequence, the material often reaches the outlet before being sufficiently ground and dispersed. This problem is further aggravated by the tendency of the grinding medium to gather at the downstream end of the vessel so that an insufficient quantity of grinding medium is present throughout the length of the vessel to attain uniform dispersion of the material.